#include<stdio.h>
int main()
{
    float add(float x,float y);
    float a,b,c;
    printf("please enter a and b\n");
    scanf("%f%f",&a,&b);
    c=add(a,b);//如果没有前面哪个声明，无法判断add是不是函数名
    printf("the sum is %f",c);
    return 0;
}
float add(float x,float y)
{
    float z;
    z=x+y;
    return(x+y);
}